Circuit breaker



July 14, 1936. c. H. HILL 2,047,824

CIRCUIT BREAKER Filed April 25, 19 55 2 Sheets-Sheet l Elm Inventor" ChEr'leS H. Hil l,

is Attorney.

July 14, 1936. c. H. HILL CIRCUIT BREAKER Filed April 25, 1935 2 Sheets-Sheet 2 Patented July 14, I936 UNITED STATES PATENT OFFICE omcorr BREAKER Charles H. Hill, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York My invention relates to circuit breakers, more particularly to circuit breakers of the trip-free type in which the circuit controlling contacts are manually operable between open and closed circuit positions and. are automatically operable to open circuit position upon the occurrence of predetermined abnormal current conditions, and has for an object the provision of a circuit breaker of this type which is simple and reliable in its operation and inexpensive to construct.

It has heretofore been proposed to provide circuit breakers of this general type with suitable explosion proof, arc extinguishing devices so as to combine the protective features of a fuse and the advantages of a manually operable switch, and such circuit breakers have found considerable application in the control of distribution and feeder circuits. When applied to the control of circuits of this type, especially in industrial applications, the circuit breaker is often required to carry normal currents of considerable magnitude and to interrupt extremely large currents in case a fault or short circuit occurs in the system. The circuit breaker must therefore be provided with conducting and interrupting elements of considerable size and the circuit breaker operating mechanism must be strong and rugged, which necessitates the use of heavyoperating springs.

The forces exerted on the movable contacts of the circuit breaker due to large currents flowing therethrough tend to separate the contacts and may be of such magnitude as .to render impracticable the provision of operating springs of sufficient strength to maintain satisfactory contact pressures at the end of the closing stroke. Much is yet to be desired, therefore, in a circuit breaker of this type which is strong and rugged enough to withstand the severe operating conditions encountered and which will quickly interrupt currents of considerable magnitude without loud explosions or destructive arcing. Accordingly, it is a further object of my invention to provide a heavy duty circuit breaker of this type having an operating mechanism which is strong and rugged in its construction, which will maintain good contact pressures when the circuit breaker contacts are in the closed circuit position and which is reliable in its operation.

In carrying out my invention in one form, I provide a circuit breaker comprising relatively movable contacts and an operating mechanism therefor which includes a manually operable mechanism of rugged construction for moving the contacts between open and closed circuit positions with a snap action, and current-responsive means including a normally latched tripping arm biased by suitable tripping springs for operating the contacts to open circuit position upon the occurrence 1 of abnormal current conditions. More specifically, I provide a strong and rugged 5 operating mechanism including a pair of toggle links, one of which is a substantially triangular or three-point link arranged to act as a crank to make or break the toggle when rotated about its pivot. Overcenter spring means are provided 10 for rotating the crank to operate the toggle, and automatic tripping means are provided for rotating the crank against the force exerted by the overcenter springs to break the toggle and operate the contacts to the open circuit position upon 1 the occurrence of abnormal current conditions.

For a more complete understanding of my invention, reference should now be had to the drawings inwhich Fig. 1 is an elevational view, partly in section, of a circuit breaker embodying 20 my invention; Figs. 2 and 3 are fragmentary views of the circuit breaker shown in Fig. 1, illustrating the operating mechanism in diflerent operating positions; Fig. 4 is a plan view of a preferred type of circuit-breaker embodying my invention, the cover of the circuit breaker and certain parts thereof being removed to show the operating mechanism; and Fig. 5 is a sectional view taken along the line 5-5 in Fig. 4.

Referring now to Figs. 1, 2, and 3 of the drawings, I have shown my invention in one form as applied to a circuit breaker comprising a base Ill of molded insulation for supporting a compression chamber, arc-extinguishing device II and an operating mechanism indicated-generally by the reference numeral l2. The compression chamber H is preferably of the type described and claimed in a eopending application of Ludwig S. Walle, Serial No. 667,856, filed April 25, 1933, entitled Circuit breakers which application is assigned to the same assignee as the present invention, and for the purposes of the present invention this are extinguishing device may be described as comprising walls of pressure-resistant material enclosing a fixed contact l3 and a reciprocally movable contact I. As shown, the fixed contact I3 is supported by aninsulating bushing l5 and is electrically connected by means of a conductor Hi to a terminal screw H. The reciprocal contact I is slidably supported in the opposite end wall of the compression chamber and is electrically connected by means of a flexible conductor l8 and an L-shaped conductor l9 1 to one leg of a U-shaped bimetallic element 20,

ductor 2| to a terminal screw 22.

My improved operating mechanism 62 is supported on a U-shaped frame 23 secured in any suitable manner to the base In. Pivotally mounted on a pin 24 carried by the frame 23 is an operating member 25 provided with an insulated handle 26 arranged to extend through an aper ture 21 in the circuit breaker cover 28. Also pivoted on the pin 24 is a pair of spaced parallel arms 29 connected together intermediate their ends by a cross member til, the adjacent ends of the parallel arms remote from the pivot pin 24 carrying an operating pin 33!], the opposite ends of which extend through. slots 32 in the frame 23. The end walls of the slots 32 form stops for the pin 39 in its two positions.

In order to operate the pin ti and the arms 29 with a snap action, I provide a pair of overcenter springs 33, one only of which is shown, arranged outside of and on opposite sides of the U-shaped frame 23, one end of each spring being connected to a lug at extending laterally outward from the operating member 25 and the opposite end of each spring being connected to the operating pin 3i. As shown, the operating pin M is connected to a substantially triangular or three-point link 35 which is pivoted on a pin 36 supported by one side of the frame and connected by means of a pin 37/ to a second link 38, the opposite end oi which is suitably connected to the reciprocal contact M. The pin 3t extends inwardly from one side of the frame a short distance only and the arms 29 are arranged to move past the extending end or" the pin 36 to the position shown in Fig. 2 as hereinafter described.

It will be apparent that when the insulated handle 26 is moved toward the interrupting device it to rotate the operating member 25 about the pivot 26 in a clockwise direction as viewed in the drawings, the springs will move overcenter relative to thepivot' 2 1, and the arms 29 and the pin 38 carried thereby will be operated with a snap action to the position shown in Fig. 2, the pin 36 being brought to rest in engagement with the right hand end walls of the slots 32, whereby the link '35 is rotated about the pivot and acts as a crank to make the toggle composed or the links 35 and 3t and thereby move the reciprocal contact M to the closed circuit position. Similarly, when the handle 26 is moved away from the arc-extinguishing device 00, the link will be rotated in the opposite direction about the pivot 36 to break the toggle and move the reciprocal contact M to open circuit position.

As shown in Fig. 2, when the circuit breaker contacts are in the closed circuit position, the toggle links 35 and 38' are in straight-line relation so that any force exerted on the reciprocal contact i4 tending to open the contacts will be exerted directly on the pin 36 rather than on the overcenter springs 33, and the contact pressure will thus be maintained.

The circuit breaker is also adapted for automatic operation to open the circuit upon the occurrence of predetermined abnormal current conditions and accordingly, I provide a tripping member 39 pivotally'mounted on the pin 24 and provided with a portion Mi which extends adjacent the cross member 36 on the parallel arms 29 when the circuit breaker is in the closed circuit position shpwn in Fig. 2. As shown, the frame 23 is provided with a pair of outwardly extending portions 48, one on each upstanding the other leg of which is connected by a conleg,'between which I provide a tripping spring 42;, one end of which bears against a cross member 43 extending between the frame portions 4i and the other end of which engages a stop plate 44 carried by a push rod 46, which rod extends 5 through the spring 42 and is slidably guided in the cross member 43. The end of the push rod 46 engages a notch 41 in the tripping member 39 and the spring 52 is normally maintained under compression by a latch '48 carried by the tripping member 39 and arranged to engage a latch plate 49 secured to the free end of the bimetallic element 263.

So long as normal current is flowing in the circuit breaker, the latch lli will engage the latch plate 49 as shown in Figs. 1 and 2, and the tripping member 39 will be held against the force exerted by the tripping spring 322, and it will be observed that when the tripping member is in this latched position, the arms 29 and the oper- 2Q ating pin 36 may be operated between open and closed circuit positions without engaging the extending portion Gil on the tripping member. Upon the occurrence of abnormal current conditions, however, the bimetallic element it will be 5, heated sufficiently to move the latch plate 39 out of engagement with the latch ii? whereupon the tripping spring d2 will quickly move the tripping member 39 in a clockwise direction about the pivot 26, and the extending portion it thereof will engage the cross bar Elli and move the arms 2t and the operating pin 30 to the position shown in Fig. 3 against the force exerted by the overcenter springs 33, thereby rotating the link to break the toggle and open the circuit breaker 35 contacts.

In order to reclose the circuit breaker after it has been opened automatically by the tripping member 39, it is necessary first to move the operating handle 26 from the position shown in Hg. 3 to the position shown in Fig. 1, during which movement a portion 50 on the operating member 25 will engage a shoulder hi on the tripping member 39 to return the tripping member to the position shown in Figs. 1 and 2 against the force exerted by the tripping spring 32. If the bimetallic element Ed has cooled sufficiently to permit the latch 33 to engage the latch plate Qt, the circuit breaker may be closed by moving the handle 26 to the position shown in Fig. 2.

Referring now to Figs. 4 and 5, I have shown a preferred form of operating mechanism embodying my invention applied to a multipole circuit breaker of the type described and claimed in a copending application of Winfield A. Atwood, Serial No. 18,138, filed April 25, 1935, which application is assigned to the'same assignee as the present invention. This circuit breaker comprises a base 52 of molded insulation provided with a pair of side walls 53 and a plurality of intermediate walls 55, 55 and 55 arranged to form a plurality of conductor receiving compartments extending lengthwise of the base. Each of the walls 54 extends from the uppermost end of the circuit breaker, as viewed in Figs. 4 and 5, to a point adjacent one of a pair of bearing blocks 5?, the purpose of which will be fully set forth later; each of the walls 55 extends from one of the bearing blocks 5? to a point adjacent a unitary trip device indicated generally by the reference numeral 58, and each of the walls 56 extends from the lowermost end of the circuit breaker to a point adjacent the other side of the trip device 58. Intermediate the ends of each conductor re- 7 ceiving compartment, 9, cross wall 59 is provided formed integrally with the base 52.

Each conductor receiving compartment is provided at its opposite ends with the terminal members 68 and 6|, respectively, and the arrangement of the conductor members and the circuit controlling contacts for completing an electric circuit therebetween being the same in each compartment, only one such arrangement will be described.

Extending from the terminal member 60 along the base 52 to the cross wall 59 is a conductor bar 62 rigidly fastened to the base in any suitable manner and connected to the terminal member 68 by a bolt 63. Disposed on the opposite side of the cross wall 59 and extending therefrom along the base 52 to the trip device 58 is a second conductor bar 64 also rigidly fastened to the base. It will be observed that the trip device 58 includes a pair of conductors 65 and 66 which are respectively connected as shown to one end of the conductor bar 64 and to the terminal 6|. The respective ends of the conductor bars 62 and 64 which are disposed adjacent the cross wall 59 are provided with contact portions 61, and a movable bridging member 68 carrying cooperating contact portions 69 is arranged to span the cross wall 59.

Each of the bridging members 68 nests within the legs of a U-shaped carrier 18 formed on one arm of a bifurcated lever H and is supported by a bolt 12 .extending therethrough, a plurality of springs 13 being arranged in aligned recesses in the bridging member and the carrier to provide uniform contact pressure. In order to reduce blistering and arcing at the contacts 61 and 69, each bridging member is provided with an arcing tip or contact 14 secured to one end of a conductor spring 15 arranged in a slot in the carrier 18 and secured thereto by a rivet 16. As shown, the end of the spring 15 which is remote from the contact 14 is electrically connected to the conductor bar 64, and the contact 14 is arranged to engage the conductor bar 62 to provide a shunt circuit around the bridging member 68, the conducting spring 15 being arranged so that when the bifurcated lever II is operated to move the bridging member to its open circuit position, the contact 14 will not be disengaged from the conductor bar 62 until after the contacts 6'! and 69 have separated, and when the bridging member is moved to its closed circuit position the contacts 61 and 69 will not engage until after the contact 14 has engaged the conductor 62.

In order to provide for the interruption of heavy currents without loud explosions or are ing, each pole of the circuit breaker is provided with an arc extinguishing device connected in parallel circuit relation with the bridging member 68, which device is preferably of the type described and claimed in a copending application of Ludwig S. Walle, Serial No. 4,448, filed February 1, 1935, which application is assigned to the same assignee as the present invention. For present purposes this are extinguishing device may be described as comprising a compression chamber, the body portion of which comprises a cylinder I1 supported on an insulating support 18 which is secured to the conductor bar 62 by a plurality of screws 19.

The cylinder TI is provided with suitable end closures as'shown, a fixed contact 88 extending through one end thereof and being electrically connected to the conductor bar 62 by an L-shaped conductor 8|. As shown, the arc extinguishing device also includes a reciprocal contact 82 which slidably extends through the opposite end wall of the compression chamber and is provided with sealing means for substantially gas-tightly seal- 5 ing the compression chamber. The sealing means comprise a plurality of washers 83 formed of suitable flexible material such as leather, and valve means comprising a shoulder 84 formed on the movable contact 82 and arranged to en- 10 gage a valve seat 85 in the end wall of the compression chamber. Threadedly connected to the extending end of the movable contact 82 is an extension 86 which is electrically connected by a flexible conductor 8'! to the conductor bar 64. 15

It will be observed that the relatively reciprocal contacts 89 and 82 are connected in parallel circuit relation with the bridging member 68 and the intermediate shunt circuit comprising the arcing contact", and in order that the final circuit-breaking action may take place within the compression chamber so as to prevent arcing at the bridging member, the other arm of the bifurcated lever II is connected to the reciprocal contact 82 by means of a resilient lost-motion 25 connection which includes a pin 88 carried by the bifurcated lever and extending through a slot in the extension 86, a suitable spring 89 being arranged within the extension 86 with its respective ends bearing against the movable contact 82 and the pin 88. This lost-motion connection is so proportioned that when the bifurcated lever H is moved between open and closed circuit position, the circuit through the compression chamber will be opened subsequent to 35 the intermediate circuit through the arcing contact 14 and will be closed prior to the closing of the intermediate shunt circuit.

In order that all of the poles of the circuit breaker may be operated simultaneously by a single operating mechanism, each of the bifurcated levers H is provided with a clamping portion 90 arranged to engage an insulated crossbar 9| which extends across the three poles of the circuit breaker and is journaled in the before-mentioned bearing blocks 51. Arranged in one of the conductor receiving compartments adjacent the crossbar 9| is the circuit breaker operating mechanism which includes a U-shaped frame 92 which is secured to one of the conductor bars 64. Pivotally mounted on a pin 93 carried by the frame 92 is an operating element 94 provided with an insulated operating handle 95 arranged to extend through a suitable aperture in the circuit breaker cover. The operating element 94 nests within the U-shaped frame 92 and is provided with the extending portions 95 which I extend laterally beyond the legs of the frame. Also pivoted on the pin 93 is a pair of spaced parallel arms 91 connected together intermedi- 0 ate their ends by a cross member 98, the adjacent ends of the arms 91 opposite from the pin 93 carrying an operating pin 99 the respective ends of which extend through slots I89 in the frame 92. Connected between the extending ends 65 of the pin 99 and the extending portions 96 of the operating element 94 is a pair of overcenter spring devices lfll, the constructional details of which are fully described in the above referred to Atwood application.

Connected between the operating pin 99 and one of the bifurcated levers H is a toggle mechanism comprising a link I82, one end of which engages the bifurcated lever H and the other end of which is pivoted to a second link I03 pivotally 75 supported on a pin IM and provided with a slot I95 through which the operating pin @9 extends. The link I03 as shown is a substantially triangular link similar to the link 35 described in connection with Figs. 1, 2, and 3.

In Fig 5, the circuit breaker is shown in the closed circuit position, and it will be apparent that when the operating handle 95 is moved to rotate the operating element 9 3 about the pivot 53, the operating mechanism will function as described in connection with Figs. 1, 2, and 3, to make and break the toggle with a snap action whereby the insulated crossbar @I will be rotated to move the circuit breaker contacts between open and closed circuit position.

The automatic tripping mechanism in this embodiment of my invention comprises a pivoted tripping member lilt and a pair of tripping springs IN, the operation of which is controlled by the trip device 58 in a manner to be more fully described. The trip device 58 includes a latch Hi8 arranged normally to engage a latch finger Hi9 secured to one end of the tripping member I95, the other end of the tripping memher being pivotally supported on the pin 93. Interm'ediate its ends the tripping member IE5 is provided with a pin Ilil, each extending end of which carries a bearing plate III arranged to engage an end of one of the tripping springs Hill, the opposite ends of which rest in depressions M2 in the conductor bar 66. Each bearing plate I I I carries a guide rod I I3 which extends through the associated tripping spring into a drilled hole IIQ which extends through the conductor bar ti l and into the base member 52.

In the closed circuit position of the circuit breaker shown in Fig. 5, it will be seen that the cross member 98 which extends between the parallel arms El is engaged by an extending portion M5 on the tripping member Iilt. Upon the occurrence of abnormal current conditions, the latch Illt of the trip device 58 will be moved in a manner to be fully described, to release the latch finger I09 whereupon the tripping'springs Itlwill quickly move the tripping member Illt about the pivot 93 in a clockwise direction as viewed in the drawings, to move the arms er and the operating pin 99 downwardly and rotate the link I03 about its pivot ltd in a clockwise direction against the force exerted by the overcenter spring devices IIlI whereby the toggle is broken and the circuit breaker contacts are operated to the open circuit position.

The circuit breaker may be reclosed after an automatic operation to the open circuit position exactly as described in connection with the circuit breakers shown in Figs. 1, 2, and 3, the operating element 941 being provided with a portion H6 arranged to engage a cooperating portion I II on the tripping member I86.

It will be apparent that in a heavy duty circuit breaker of this type, the tripping springs Iilll must exert a force of considerable magnitude and, therefore, it is necessary to provide a rugged trip device'for normally latching the tripping member Ittagainst the force exerted by the springs. Accordingly, the trip device 58 is preferably of the type described and claimed in a copending application of John L. Lappin, Serial No. 4,659, filed February 2, 1935, entitled Circuit breakers which application is assigned to the same assignee as the present invention.

This trip device may be described for the purposes of the present application as comprising a subbase II8 which is preferably formed separate between the terminal members til and SI.

from, and rigidly secured to the base 52. Supported centrally of the subbase M8 is a frame having a pair of spaced walls I I9 between which are supported a latch plate I20 pivoted at I2I, a. U-shaped impact member I22 pivoted at I23 and a U-shaped reset member I24 pivoted at I25. The latch plate I20 carries the previously referred to latch I08, and the IJ-shaped impact member I 22 is overturned to provide a striking surface I26 for engaging a portion I2'I of the latch plate to impart a hammerlike blow thereto. Each leg of the impact member I22 carries a pin I28 extending through a slot I29 in one of the supporting walls I I 9 and arranged to engage a cam finger I30 provided on the U-shaped reset member I24, the yoke portion of which is interposed in the path of the tripping member Idt. The impact member I22; is normally held in the position shown in Fig. 5 by a trip bar I3I which extends across the three conductor receiving compartments of the circuit breaker and is pivoted on pins I3Ia, the trip bar being normally biased by a spring I32 (Fig. 4) into engagement with a finger I33 carried by the impact member.

Associated with the conductors in each conductor receiving compartment of the circuit breaker is a thermal and a magnetic device for moving the trip bar Iiil about its pivot, to release the impact member I22 upon the occurrence of abnormal current conditions. Each thermal device comprises a bimetallic element ltd, one end of which is fastened to and adapted to be heated by a heater strip: I35, the ends of which are respectively connected to the previously referred to conductors I55 and 65 in the circuit extending The other end or" the bimetallic element I34 is arranged adjacent an adjustable insulating button I36 secured to the trip bar Itl, and it will be apparent that when the bimetallic element I35 is heated sufficiently upon the occurrence of an overload, the bimetallic element will flex and engage the button I36 to move the trip bar ISI about its pivot.

Each of the magnetic devices comprises a U- shaped magnetic member IEII which partially encircles one of the conductors @Ii so that a magnetic fiux will be induced in the member ISI upon the flow of current through the conductor. Arranged adjacent the U-shaped magnetic members I37 is a common armature I it also pivoted on the pins I SIa, which armature extends across the three conductor receiving compartments and is provided with an extending finger I39 (Fig. 4) arranged to engage an adjustable screw Mt extending from the pivoted trip bar It I, to move the trip bar upon the occurrence of a sufiiciently high overload in one or more of the circuit breaker poles to cause the armature to be attracted by one or more of the U-shaped magnetic members I31.

It will be apparent that upon the occurrence of abnormal current conditions the trip bar I3I will be moved either by the thermal or by the magnetic means, depending upon the character of the abnormal current conditions, to release the impact member I22 for operation in a counterclockwise direction about its pivot I23 by suitable biasing springs MI, to strike the latch plate I28 a hammerlike blow and release the tripping member IllIi. When the tripping member IDS is moved to tripping position by the tripping springs llll, the U-shaped reset member I24 will be released for operation in a counterclockwise direction about its pivot I25 under the force exerted by suitable resetting springs I42 (Fig. 4) and the cam fingers I30 will thereupon engage the pins I28 extending from the impact member I22 to return the impact member to its normal position.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit breaker comprising a pair of relatively movable contacts, a frame, an operating member pivotally supported on said frame, a contact actuating toggle having one end operatively connected to one of said contacts and the other end pivoted on said frame, overcenter spring means connected to said operating member for exerting a force on the knee point of said toggle for making and breaking said toggle to actuate said one contact between open and closed circuit positions with a snap action, a tripping arm pivotally mounted on said frame, means including a tripping spring for biasing said tripping arm from one position to a second position, means including a latch for normally restraining said tripping arm in said one position, means for releasing said latch, and means responsive to movement of said tripping arm to said second position for breaking said toggle against the force exerted by said overcenter spring means.

.2. A circuit breaker comprising a pair of relatively movable contacts, -a frame, an operating member pivotally supported on said frame, a contact actuating toggle having one end operatively connected to one of said contacts and the other end pivoted on said frame, overcenter spring means connected to said operating member for exerting a force on the knee point of said toggle for making and breaking said toggle to actuate said one contact between open and closed circuit positions with a snap action, a tripping arm pivotally mounted on said frame, means including a tripping spring for biasing said tripping arm from one position to a second position, overload current responsive means for normally restraining saidtripping arm in said one position and for releasing said tripping arm upon the occurrence of predetermined abnormal current conditions, and means operated by movement of said tripping arm to said second position for breakingsaid toggle against the force exerted by said overcenter spring means.

3. A circuit breaker comprising a pair of relatively movable, contacts, a frame, an operating member pivotally supported on said frame, a contact actuating toggle having one end operatively connected to one of said contacts and the other end pivoted on said frame, one link of said toggle comprising a crank lever, overcenter spring means connected between saidoperating member and said crank lever for making and breaking said toggle to actuate said one contact between open and closed circuit positions with a snap action, a pivoted tripping arm normally biased from one position to a second position, means including a latch for normally holding said tripping arm in said one position against said bias, means for releasing said latch, and means operated by movement of said tripping arm to said second position for moving said crank lever against the force exerted by said overcenter spring to break said toggle.

4, A circuit breaker comprising a pair of relatively movable contacts, a frame, an operating member pivotally supported on said frame, an arm having an end thereof pivoted on said frame, a substantially triangular link pivoted on said frame and operatively engaging the free end of said arm, a second link pivotally engaging said triangular link and operatively connected to one of said contacts, said two links forming a contact actuating toggle, overcenter spring means connected between said operating member and said arm for making and breaking said toggle to actuate said one contact between open and closed circuit position, a tripping member provided with a portion adapted to engage said arm, a tripping spring normally biasing said tripping member from one position to a second position, means including a latch for holding said tripping member in said one position, and means for releasing said latch whereby said tripping member is operated to said second position by said tripping spring to operate said arm and break said toggle against the force exerted by said overcenter means.

5. A circuit breaker comprising a pair of relatively movable contacts, an operating mechanism comprising a U-shaped frame, an operating member pivotally supported on said frame, a pair of spaced parallel arms having adjacent ends pivotally supported on said frame, an operating pin carried by the other ends of said holding said tripping arm in said one position,

and current responsive means for releasing said latch whereby said tripping arm is moved to said second position by said spring means, a portion of said tripping arm being disposed to engage said parallel arms to move said operating pin and break said toggle against the toggle making force exerted by said overcenter springs.

6. A circuit breaker comprising a pair of relatively movable contacts, an operating mechanism comprising a U-shaped frame having a pivot extending between the legs thereof, an operating member mounted on said pivot between said legs, portions of said operating member extending beyond said legs, a pair of spaced parallel arms having adjacent ends mounted on said pivot, an operating pin supported by said arms adjacent the other ends thereof, the ends of said operating pin extending through slots in said legs of said frame, a second pivot supported by said frame, a crank lever mounted on said second pivot having a portion thereof engaging said operating pin, a link operatively connected to said crank lever and to one of said contacts, said link and said crank lever forming a contact actuating toggle, a pair of overcenter springs arranged outside of said U-shaped frame the respective ends thereof being connected to the ends of said operating pin and to said extending porspring biased tripping means for moving said pin 75 against the force exerted by said over-center spring means to break said toggle and open said contacts independently of said overcenter springs.

'7. A circuit breaker comprising a pair of relatively movable contacts, an operating mecha. nism comprising a frame, an operating member pivotally supported on said frame, an arm having one end pivoted on said frame, a. crank lever pivoted on said frame having a portion" engaging the free end of said arm, a link operatively connected to one ofsaid contacts and to said crank lever, said link and said crank iever form ing a contact actuating toggle, e pair of over= center springs connected between said free end of said arm and said operating member for meizing and breaking said toggle, a pivoted tripping member having a. portion arranged to engage said arm, a tripping spring for biasing said tripping member against said arm so as normally to bias said toggle to broken position, and current responsive means for normally latching said tripping member out of engagement with said arm'so that said operating member is free to operate. said toggle independently of said tripping member, said current responsive means being arranged to release said tripping member upon the occurrence of predetermined abnormal current conditions to break said toggie and open said contacts inde- 

